Fatal error: uncaught error: call to undefined function mysql_real_escape_string()

Fatal error: Uncaught Error: Call to undefined function mysql_real_escape_string() in C:\xampp\htdocs\webdua\pusing\xxx\proses.php:7 Stack trace: #0 {main} thrown in C:\xampp\htdocs\webdua\pusing\xxx\proses.php on line 7

<?php
	$username = $_POST['user'];
	$password = $_POST['pass'];

	$username = stripcslashes($username);
	$password = stripcslashes($password);
	$username = mysql_real_escape_string($username);
	$password = mysql_real_escape_string($password);

	mysql_connect("localhost", "root", "");
	mysql_select_db("masuk");

	$result = mysql_query("select * from pengguna where username = '$username' and password = '$password'")
				or die("failed to query ".mysql_error());
	$row = mysql_fetch_array($result);
	if ($row['username'] == $username && $row['password'] == $password){
		echo "Login sukses ".$row['username'];
	}else{
		echo "failed to login";
	}
?>